Alkali metals, and among them especially sodium, have long been established in organic chemistry as reagents, for example for the production of alcoholates, for Darzens glycidic ester condensation, for the Birch reduction for conversion of aromatic to aliphatic compounds, or to acyloin condensation of esters to α-hydroxycarbonyl compounds (K. Rühlmann Synthesis (1971), 1971 (5), 236-253). In particular, the latter reaction is of importance in organic chemistry for the intramolecular cyclization of dicarboxylic acid esters to medium and large ring systems.
Another major field of application for elemental alkali metals is offered by the Wurtz coupling or Wurtz synthesis discovered in 1854 by French chemist Adolphe Wurtz, which initially served primarily for the synthesis of (cyclo)alkanes from haloalkanes. By means of the Wurtz synthesis, cycloalkanes having a ring size of from three to six carbon atoms are accessible. The Wurtz coupling is also the main route for the production of σ-π-conjugated silicon polymers through the polycondensation of halosilanes in aprotic organic solvents (R. D. Miller, J. Michl Chemical Reviews (1989), 89 (6), 1359-1410).
According to the current state of the art, the reactions above are performed in a semibatch process (described inter alia in the patents EP 0 123 934 B1, EP 0 632 086 B1, EP 0 382 651 A1, EP 1 769 019 A1, DE 10 2012 223 260 A1, EP 2 872 547 A1, EP 0 230 499 B1, JP 3087921 B2, JP 2736916 B2, CN 103 508 869 B, U.S. Pat. Nos. 4,324,901 A, 4,276,424 A). For this purpose, the suspension of an alkali metal (for example sodium) is charged in a reaction vessel. The substances to be coupled (haloalkanes, halosilanes or diesters/esters) are metered thereto under strictly controlled conditions, However, this method has a number of safety risks and procedural problems. On the one hand, the handling of the liquid alkali metals, but also of some of the reactants, such as the highly reactive chlorosilanes, on an industrial scale is very complex. Thus, moisture must be excluded completely at any rate. On the other hand, since the reaction is highly exothermic, the reproducibility of the product characteristics is influenced even by small variations within different batches. For example, even on a laboratory scale, a poor reproducibility of the results of a Wurtz coupling for the preparation of polysilanes is observed.
Since reactions with alkali metal dispersions are interfacial reactions, a dispersion as finely divided as possible and therefore a high particle surface are advantageous for quick and complete reactions. However, for a semibatch process, this is difficult to adjust exactly in production, resulting in disparities in the process. Also, an exact dosing of the reactants (for example, halogen compounds, esters) is essential for precise reaction control because different dosages can lead to deviations in the temperature course. For the above reasons, it is easy to understand that these factors also make the scaling-up of the semibatch process and the associated large-scale use of the reaction considerably more difficult.
For the reaction of alkali metals with alcohols above the melting point of the metals, a microreactor with a static mixer and heat exchanger with channel dimensions of around 500 μm was used in EP 1 162 187 B1.
The use of SDRs is prior art for the epoxidation of substituted cyclohexanones EP 1 206 460 B1, conversions of car boxy acids and esters WO 2002/018328 A1, the preparation of nanoparticles U.S. Pat. No. 8,870,998 B2, for the hydrogenation of nitrile rubber in solution EP 1 862 477 B1, for heterogeneously catalyzed reactions EP 1 152 823 B2, and for carrying out free-radical emulsion polymerizations U.S. Pat. No. 7,683,142 B2.
In addition, applications for the production of titanium dioxide particles are described in the scientific literature (S. Mohammadi; A. Harvey; K. V. K. Boodhoo Chemical Engineering Journal (2014), 258, 171-184), for the cationic polymerization of styrene using an immobilized catalyst (K. V. K. Boodhoo; W A E Dunk; M. Vicevic; R. J. Jachuck; V. Sage; D. J. Macquarrie, J. H. Clark Journal of Applied Polymer Science (2006), 101 (1), 8-19), for the photopolymerization of n-butyl acrylate (K. V. K, Boodhoo; W. A. E. Dunk; R. J. Jachuck ACS Symposium Series (2003), 847 (Photoinitiated Polymerization), 437-450), as well as for the production of mayonnaise (M. Akhtar; B. S. Murray, S. Dowu Food Hydrocolloids (2014), 42(S), 223-228), apple juice concentrate (M. Akhtar, P. Chan, N. Safriani, B. Murray, G. Clayton, Journal of Food Processing & Technology (2011), 2 (2), 1000108), and ice cream base emulsions (M. Akhtar; I. Blakemore; G. Clayton, S. Knapper, International Journal of Food Science and Technology (2009), 44 (6), 1139-1145). Furthermore, the company Flowid has realized a lithium halogen exchange at room temperature with a product flow of 100 kg/h of raw material or 20 kg/h of product for Biogen (http://www.flowid.nl/successful-scale-up-of-butyl-lithium-using-the-SpinPro/08.08.2015). In addition, many examples relating to recrystallization or particle synthesis are described in the literature. The benefits of SDR technology for these multiphase systems were discussed in detail in the literature and documented with examples (K. Boodhoo & A. Harvey, Process Intensification for Green Chemistry: Engineering Solutions for Sustainable Chemical Processing (2013), Chapter 3, John Wiley & Sons Ltd, pp 59-90), S. D. Pask, O. Nuyken, Z. Cai, Polymer Chemistry (2012), 3, 2698), P. Oxley, C. Brechteisbauer, F. Ricard, N. Lewis, C. Ramshaw, Industrial & Engineering Chemistry Research (2000), 39 (7), 2175-2182).